I'm a user as well, so if I can't help then a dev can, but are you talking about your stream is lagging or the actual game? If you mean the stream then I'll tell you what I've done to make my stream smoother. First, if your bitrate is fine (audio bitrate as well) then try making sure you have the settings in "Advanced" set to Veryfast or Best Speed. Also, in "Video" try using Resolution Downscale and setting it to 1.25 or 1.50. I kept having issues until I set my Resolution Downscale to 1.50 and now my stream is just fine. It won't make the quality awful, though it might be a little lower, but all it really does is downscale the video before it's encoded which takes a load off of the CPU. Also, set your FPS no higher than 30 because your internet won't be able to handle higher. I have 4Mbps up and still have to use 30 fps or lower.
If your game itself is lagging, try making sure nobody else is using the internet. The lower your upload speed, the harder it is to do multiple things online without something else being interrupted. Can't really do that much to help improve game lag other than faster internet and if you're like me you can't just run out and buy amazing internet with extremely good upload.
Hope I could help somewhat, if not then hopefully someone else can. Cheers and good luck streaming! :D
